Re: Using PPC asm (from Linux kernel) in xine
On 22 May, this message from Albert D. Cahalan echoed through cyberspace:
> Michel Lanners writes:
>> On 22 May, this message from Albert D. Cahalan echoed through cyberspace:
>>> =?iso-8859-1?Q?Rog writes:
>
>> [about fast memcopy in asm]
>>
>>> dcbt eight,src /* prefetch the next cache line */
>>> loop_top:
>>> dcba eight,dst /* allocate a cache line */
>>> lfd f11,8,(src)
>>> lfd f12,16,(src)
>>> lfd f13,24,(src)
>>> lfdu f14,32,(src)
>> ^^
>> These should probably be 0,8,16 and 24... same goes below.
>
> Nope. I thought so too, but then lfdu would increment
> the pointer by only 24.
Got me. Thought the 'u' part was some kind of cache flush thing (like
some altivec ops have). Thanks for showing me how little PPC asm I know
;-))
>> And don't forget the loop counter and some increment...
>> Or code it with a decrement operator and copy backwards?
>
> I didn't forget; look again. This is PowerPC. :-)
> Here's the assembly with C code:
>
> dcbt eight,src // prefetch the cache line with src[1]...src[4]
> loop_top: do{
> dcba eight,dst // allocate a cache line for dst[1]...dst[4]
> lfd f11,8,(src) double_1 = src[1];
> lfd f12,16,(src) double_2 = src[2];
> lfd f13,24,(src) double_3 = src[3];
> lfdu f14,32,(src) double_4 = src[4]; src += 4;
> dcbi r0,src // would like to discard the src[-3]...src[0]
> dcbt eight,src // prefetch the cache line with src[1]...src[4]
> stfd f11,8,(dst) src[1] = double_1;
> stfd f12,16,(dst) src[2] = double_2;
> stfd f13,24,(dst) src[3] = double_3;
> stfdu f14,32,(dst) dst[4] = double_4; dst += 4;
> dcbf r0,dst // write back dst[-3]...dst[0] if needed, then invalidate it
> bdnz loop_top }while(--ctr);
OK, but then you're not showing initialization of ctr, are you?
Cheers
Michel
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